New York City’s 911 call system will come under new scrutiny after City Comptroller John Liu announced on Tuesday that he will conduct an audit of the emergency network to investigate several recent crashes.

Mr. Liu, a Democratic candidate for mayor, is the latest person vying for the city’s top office to voice concern over the new dispatch system, which was fully launched on May 29 and has since seen several glitches in communicating emergency calls to the appropriate first responders. Next Monday, the City Council will hold a hearing on the issue.

Police and fire officials have defended the new system, called ICAD, as a necessary upgrade to an antiquated network, and they said that they expected that an overhaul using new technology would experience minor interruptions.

“Based on all the information I have, it is working, it is working well,” New York Police Department Commissioner Raymond Kelly said on Tuesday. “You’re going to have a couple of exceptions as kinks get worked out.”

Mr. Kelly, whose department is responsible for the network, said contractors who designed the system are posted 24 hours a day to assist in its use.

The Russo family

Ariel Russo

While there have been no reported deaths or injuries attributed to any of the glitches, the delay in sending an ambulance to assist a 4-year-old who was struck by a teenage driver allegedly eluding police last week has shown a harsh light on the new system. Fire Department officials said the delay in sending an ambulance to help Ariel Russo was caused by human error by the call taker and was unrelated to the new system.

Meanwhile, the union representing 911 call takers has charged that the city was passing the blame for the system’s problems.

On Tuesday, Fire Department Commissioner Sal Cassano said an investigation is underway into the allegations.

Mr. Cassano said “that’s part of my investigation, to bring people in, everybody that was working on the floor that day, including the supervisors, to see what they saw, to see what they were doing, and then we will get down to the bottom of it.”

Mr. Liu said the audit will examine the glitches and whether any of them could be traced to the delay in getting help to Ariel.

“Lives are at stake,” Mr. Liu said in a news release. “New Yorkers need an E911 system that works, and they need it now.”

Mr. Liu has previously been critical of the 911 upgrade process. Two previous audits conducted by his office charged that the overhaul went grossly over-budget and several years behind schedule.